Practical Electron Microscopy and Database

Base-centered orthorhombic structure can be formed by Coincident Site Lattice (CSL). It is known two FCC lattices can rotate about [110] by an angle θ and allow to interpenetrate through each other to form a dichromatic boundary. At some angles θ, the pattern contains sites shared by both lattices. At such angles, the coincident sites themselves form a lattice, named as CSL, which for the [110] axis is base-centered orthorhombic.

The TiSi₂ formed by solid state reaction of between Ti and Si films has two different structures: the C49 (base-centered orthorhombic) structure formed between 450 °C and 650 °C, and the C54 (face-centered orthorhombic) structure formed above 650 °C. The C49 TiSi₂ is a metastable phase and is usually the first crystalline phase to form in the reaction between Ti and Si, while the C54 TiSi₂ phase is a stable phase, having a lower electrical resistivity than the C49 phase. Both crystal structures have similar atomic arrangements with a hexagonal array of Si atoms around Ti atoms at the center, but the staking arrangement of the unit cells are different:  the C49 phase has a two-layer repeat while the C54 phase has a four-layer repeat.